A pixel cell with increased dynamic range is formed by providing a floating diffusion region having a variable capacitance, controlled by at least one gate having source and drain regions commonly connected to the floating diffusion region. The gate has an intrinsic capacitance which, when the gate is activated, is added to the capacitance of the floating diffusion region, providing a low conversion gain readout. When the gate is off, the floating diffusion region capacitance is minimized, providing a high conversion gain readout. The gate may also be selectively switched to mid-level. At mid-level, a mid-level conversion gain, which is between the high and low conversion gains, readout is provided, but the gate still provides some capacitance to prevent the floating diffusion region from saturating.
Legal claims defining the scope of protection, as filed with the USPTO.
1. An imager system comprising: a pixel array comprising a plurality of pixels, each pixel comprising: a photosensor; a first storing means for receiving and storing charges from the photosensor; a storage-changing means for changing the capacitance of the first storing means, wherein the storage-changing means is operable to receive a first control signal that turns the storage-changing means only partially on, wherein the storage-changing means is operable to receive a second control signal that turns the storage-changing means on, wherein the first control signal is at a first voltage level, and wherein the second control signal is at a second voltage level that is greater than the first voltage level; and a readout means for providing at least one pixel output signal that corresponds at least to a charge stored in the first storing means while said storage-changing means is turned only partially on; and an image processor for producing an image signal based on the output signals provided by the pixels.
2. The imager system of claim 1 , where, when the first control signal is received by the storage-changing means, only a portion of an intrinsic capacitance of the storage-changing means is added to a capacitance of the first storing means.
3. An imager system comprising: an image processor; and an imaging device coupled to the processor and comprising a pixel array comprising a plurality of pixels each of the pixels comprising: a photosensor; a charge-storing means for receiving and storing charges from the photosensor; a storage-changing means for selectively changing the capacitance of the charge-storing means, wherein the storage-changing means has an intrinsic capacitance; a controlling means for causing the storage-changing means to add or remove at least a portion of intrinsic capacitance of the storage-changing means to the capacitance of the storing means, wherein the controlling means is operable to apply a first control signal to the storage-changing means that turns the storage-changing means only partially on, wherein the controlling means is operable to apply a second control signal to the storage-changing means that turns the storage-changing means on, wherein the first control signal is at a first voltage level, and wherein the second control signal is at a second voltage level that is greater than the first voltage level; and a readout means for providing an output signal during a portion of a readout period, wherein the output signal is output while said storage-changing means is turned only partially on.
4. The imager system of claim 3 , wherein the controlling means, when the first control signal is applied to the storage-changing means, adds only a portion of intrinsic capacitance of the storage-changing means to the capacitance of the storing means.
5. A method of operating an imaging system, wherein the imaging system comprises a photosensor, a charge storage node having a capacitance, and a capacitive structure that has a capacitance and that, in response to control signals, selectively changes the capacitance of the charge storage node, the method comprising: with the photosensor, converting incident light into an electrical charge; transferring the electrical charge from the photosensor to at least the charge storage node; applying a first control signal to the capacitive structure that partially activates the capacitive structure such that: when the electrical charge has a magnitude that is below a threshold level, the capacitance of the charge storage node is not substantially increased by the capacitance of the capacitive structure and the electrical charge is stored substantially entirely by the charge storage node; and when the electrical charge has a magnitude that is above the threshold level, the capacitance of the charge storage node is increased by a portion of the capacitance of the capacitive structure, a first portion of the electrical charge is stored in the charge storage node, and a second portion of the electrical charge is stored in the capacitive structure; and applying a second control signal to the capacitive structure that activates the capacitive structure such that the capacitance of the charge storage node is increased by the capacitance of the capacitive structure, wherein the first control signal is at a first voltage level and wherein the second control signal is at a second voltage level that is greater than the first voltage level.
6. The method defined in claim 5 wherein the capacitive structure comprises a gate structure, a source region, and a drain region, wherein the source and drain regions are both connected to the charge storage node, and wherein applying the control signal to the capacitive structure comprises applying the control signal to the gate structure of the capacitive structure.
7. The method defined in claim 5 wherein the charge storage device comprises a floating diffusion node, wherein the capacitive structure comprises a gate structure, a source region, and a drain region, wherein the source and drain regions are both connected to the charge storage node, and wherein applying the control signal to the capacitive structure comprises applying the control signal to the gate structure of the capacitive structure.
8. The method defined in claim 5 wherein transferring the electrical charge from the photosensor to at least the charge storage node comprises transferring the electrical charge from the photosensor to the charge storage node and the capacitive structure while applying the second control signal to the capacitive structure.
9. The method defined in claim 8 wherein applying the first control signal to the capacitive structure to partially activate the capacitive structure comprises applying the first control signal after transferring the electrical charge from the photosensor to the charge storage node and the capacitive structure while applying the second control signal to the capacitive structure.
Cooperative Patent Classification codes for this invention. Click any code to explore related patents in that topic.
June 19, 2006
August 2, 2011
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